Ignition system



P. A. BLACKINGTON ETAL 3, 5,704-

March 17, 1964 IGNITION SYSTEM 2 Sheets-Sheet 1 Original Filed May 16, 1960 INVENTORS PAUL A. BLACKINGTON By mmcz W.BURGHER\ 5 4! fi rwii M 1964 P. A. BLACKINGTON ETAL 3,125,704

IGNITION SYSTEM Original Filed May 16, 1960 2 Sheets-Sheet 2 INVENTORS PAUL A. BLACKINGTON MAURICE W. BURGHER ATT NEYS United States Patent 3,125,704 IGNITION SYSTEM Paul A. lllackington and Maurice W. Burgher, Sidney, .N.Y., assiglers to The Bendix Corporation, idney,

N.Y., a corporation of Delaware Continuation of application Ser. No. 29,280, May 16, 1960. This application Feb. 2, 1962, Elm. No. 172,375

15 Qlahns. (Cl. 315-209) This invention relates to a novel ignition system which provides a succession of spark gap discharging pulses to a spark gap. The ignition system of the invention may be used to advantage, for example, in internal combustion engines of the jet or ram jet type.

This application is a continuation of application Serial No. 29,280, filed May 16, 1960, now abandoned.

The invention has among its objects the provision of a novel ignition system which may be continuously operated without damage to a spark discharge device supplied thereby or to parts of the ignition system.

A further object of the invention lies in the provision of an ignition system of the type indicated wherein there are provided two power sources, one of which may be employed at certain critical times in the operation of an engine and the other of which may be employed as a continuously operating stand-by source of ignition spark discharges.

Yet another object of the invention lies in the provision of an ignition system which selectively supplies ignition needs of an engine or the like from a direct current power source and which provides continuously operating standby ignition powered from an alternating current source.

A still further object of the invention lies in the provision of an ignition system of the type indicated wherein the direct current source and the elements of the ignition system operated thereby are of large capacity, whereby to provide spark discharges of high energy, as for taking off and landing operations of an aircraft, and the continuously operating stand-by ignition portion of the systern supplies spark discharges of substantially lower energy content and may be operated continuously without dam- I age to any of the elements of the system.

The above and further objects and novel features of the invention will more fully appear from the following description when the same is read in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are for the purpose of illustration only, and are not intended as a definition of the limits of the invention.

In the drawings, wherein like reference characters refer to like parts throughout the several views,

FIG. 1 is a circuit diagram for a preferred embodiment of ignition system in accordance with the invention; and

FIG. 2 is a circuit diagram for an alternative embodiment of ignition system in accordance with the invention.

Engines of the jet or ram jet type are customarily ignited by an ignition system which supplies a succession of spark gap discharging pulses to a spark gap device positioned within the engine. Although a jet engine will normally continue to operate when once ignited, even though the ignition system is then shut oif, it is much safer to operate a jet aircraft with the ignition system thereof in continuous operation, since this guards against flame-out of the engine which may be dangerous at any time.

The illustrative embodiments of the present invention provide an ignition system in which electrical spark discharges of high intensity are generated when desired, as during take off and landing of an aircraft, and which further provides continuous stand-by spark discharges of appreciably lower intensity at all other times. If, there- 3,125,704 Patented Mar. 17, 1964 fore, flame-out should accidentally occur, the engine will readily be started again almost immediately by the standby ignition discharges. In the specific embodiment shown, the high intensity spark discharges for initial operation of the engine are provided from a direct current source such as a battery, and the lower intensity, stand-by spark discharges are provided by an alternating current source, such as an alternating current generator which may be either air driven or driven by the jet engine once it has started.

In the embodiments shown, the spark discharges for initial operation of the engine are provided by a direct current source such as a battery, and the stand-by spark discharges are provided by an alternating current source, such as an alternating current generator which may be either air driven or driven by the jet engine once it has started. It is disadvantageous to maintain the direct current supply for the ignition system in continuous operation because of the consequent wear of the vibrator and because the transformer fed by the vibrator would become unduly heated if it were continuously operated from the direct current source. The present invention overcomes such difiiculties, while still providing a continuous, stand-by source of electrical discharges, by providing a further alternating current power source, so that the vibrator need not be operated when the ignition circuit is powered by such alternative source. Such alternative, alternating current source also is advantageous, since the heating of the transformer in such alternative current source during continuous operation of the circuit does not exceed feasible limits.

Turning now to the drawings, the ignition system shown in FIG. 1 is made up of two main units, the first, at the top of the figure, being a direct current powered unit, designated 12, adapted for intermittent use, and the second, designated 37, being an alternating current powered unit adapted for continuous operation. The two units are interconnected in a manner to be described and alternatively supply high voltage electrical pulses to a spark discharge device such as an engine igniter plug indicated at 36. The construction of the units and their manner of interconnection are such that the operation of either while the other is inactive does not adversely affect the inactive unit nor decrease the efficiency of the active unit.

Unit 12 is provided with a source of direct current such as a battery 10 which is selectively connected to the unit by a switch 11. Unit 12 has a conventional radio filter 14 which includes a choke coil and condensers, as shown. From filter 14 the ungrounded lead wire 13 extends to the vibrator coil 15, being connected to one end of each of the two windings of coil 15 and the primary of a step-up transformer 17. The left hand winding of coil 15 is the so-called running winding, and the right hand winding is a bias winding." Coil 15 is provided with a vibrator provided with contacts 16 which are alternately opened and closed by the vibrator. The thus produced current surges through the primary of transformer 17 inducing alternating voltage in the secondary of transformer 17. The alternating voltage from such secondary is led by a wire 23 to a plurality (two shown) of serially connected rectifier tubes 19. The voltage fed from the rectifier tubes through wire 33 is thus in a form of a series of unidirectional pulses.

Wire 33 is connected to one side of a storage condenser 20, the other side of the condenser 20 being connected to ground. A resistance 21 is connected in shunt with condenser 20 as shown. Beyond condenser 20 and resistance 21, wire 33 leads to a first control gap 22 which may, for example, have a discharge voltage of 3000 volts, the voltage at which it is desired to operate the primary of a step-up transformer feeding the spark discharge device. Control gap 22 is shunted by a condenser 24, as

3 shown. Beyond control gap 22, the lead wire, there designated 38, is connected to ground through a resistance 25. Beyond resistance 25 wire 38 leads to a second gap device 26 which may, like gap 22, incorporate spaced elec trodes sealed within an envelope. Gap 26 is of such construction that its discharge is substantially lower than that of control gap 22, the discharge voltage of gap 26 being, for exarnple, 1000 volts. A condenser 27 is shunted across gap 26 as shown. A resistance 29 is connected to ground at one end thereof and at the other end is connected to the main lead wire beyond gap 26.

Such main lead wire, beyond resistance 29, is connected to one end of each of the primary 31 and the secondary 32 of a high frequency step-up transformer 39. The other end of primary 31 is connected to ground through a condenser 34. The lead wire 35 from the other end of the secondary 32 is brought out through a conventional connection to one terminal of the igniter plug 36.

In a typical installation in accordance with the invention, the components of unit 12 are such as to provide spark discharges with an energy content of joules, which is ideal for use in starting an engine. Unit 12 is placed in operation by closing switch 11 whereby storage condenser 20 is charged in the manner above described. When the charge on condenser reaches the break-down voltage of control gap 22, condenser 25) discharges across such gap. Because the further discharge gap 26 has a break-down voltage which is appreciably less than that of gap 22, a discharge once started across gap 22 continues until condenser 24? has become substantially discharged. Such discharge through gaps 22 and 26 upon flowing through primary 31 of coil 33 induces a high tension pulse in secondary 32, such pulse being led to spark discharge device 35. It will be seen that the further spark gap 25, its shunting condenser 27, and the resistance 29, which are interposed in unit 12, do not sub-. stantially alter the interaction of the control gap 22 and the step-up transformer when the spark discharge device 35 is powered by unit 12. Element 27 functions to prevent undesirable flow of current into unit 12 from unit 37 when the spark discharge device 36 is powered by the latter unit.

Unit 37 is an alternating current powered source of high tension pulses designed for continuously powering igniter plug 36. Unit 37 may be such, for example, as to supply plug 36 with spark discharges having an energy content of 4 joules so as to provide stand-by ignition while avoiding undue heating of the components and erosion of the igniter plug.

Unit 37 is supplied by a source of alternating current such as an engine-driven or air-driven alternator 39. Alternator 39 may be, for example, one supplying 400 cycle per second current at 115 volts. Alternator 39 is selectively connected to unit 37 through a switch 46, the power input being led through a conventional radio filter unit 41 including serially connected choke coils and condensers connected to ground and to the main lead wire on opposite sides of the serially connected choke coils. The main, ungrounded lead wire from unit 41 is connected to one end of the primary of a voltage step-up transformer 42, the other end of such primary being connected to ground. One lead wire 43 from the secondary of transformer 42 is branched as shown, one branch 51 having two serially connected rectifier tubes 45 interposed therein, and the other branch 48 having two rectifier tubes 44 interposed therein, tubes 44 being disposed oppositely from tubes 45.

Beyond the second rectifier tube 44 a current limiting resistance 53 is interposed in wire 48. Connected across wires 48, beyond resistance 53, and 51, beyond the rectifier tubes, are two condensers 4s and 4'7 connected in series. A wire 49, connected to the other end of the econdary of transformer 42, is connected between condensers 46 and 47. A further condenser 52 is connected across wires 51 and 48. The described banks of rectifiers and condensers 46, 47, and 52 constitute a voltage doubling tank condenser system which functions as a storage condenser. Beyond condenser 52, wire 51 is connected to wire 48 by a resistance 54. Beyond the point of connection of resistance 54, wire 48 leads to one electrode of a control gap 55, the other electrode of such gap being connected to ground as shown. Units 12 and 37 are interconnected by a shielded wire which is connected to the two units through connectors 60 and 61, respectively. Lead wire 51 of unit 37 is connected to central lead wire 59, the central lead wire being connected to a further wire 62 in unit 12, wire 62 being connected to lead wire 38 of unit 12 between resistance 29 and the common connection between the primary and secondary of transformer 36*. The sheath 57 of the connecting lead is con nected to the grounded metallic casings of the units 12 and 37. Lead wire 51 of unit 37, before its connection to connector 61, is connected to ground through a resistance 56.

When the ignition system of the invention is powered by a unit 37, switch 49 is closed and switch 11 is opened. Such switches may, if desired, be interconnected so that when the one is closed the other is opened. The alternating current then impressed upon the primary of transformer 42 induces an increased voltage in the secondary of such transformer. The resulting secondary current is rectified by rectifier elements 44 and 45 so as to charge the tank condenser system 46, 47, and 52 in a step-bystep manner. In the illustrative system, the control gap 55 will have a break-down voltage which is substantially the same as that of control gap 22, that is, in the preferred example, 3000 volts. When the charge on the tank condenser system reaches 3000 volts, a discharge occurs across the electrodes of control gap 55. Such current discharge flows in a number of paths: (1) from control gap 55 to ground, through wire 51, to condenser 52 and back to gap 55; (2) from control gap 55 to ground, to condenser 34, through primary 31, through Wires 52, 59, and 51 to condenser 52 and back to gap 55; and (3) from control gap 55 to ground, to igniter gap 36, through secondary 32, wires 62, 59, and 51 to condenser 52, and back to gap 55. Flow of current from control gap 55 in the last named path forms a spark discharge at igniter gap 36.

During such operation of the system, the series connected condensers 27, 24, and 2th in unit 12 act as a condenser voltage divider which functions effectively to prevent current flow in unit 12 other than to the spark dis charge device 36 and through transformer 30, as described. The network made up of condensers 27, 24, and 219 limits the voltage applied to gaps 22 and 26 to one which is less than the ionization or break-down voltage of these gaps as connected in series. Thus gap 22 cannot ionize to form an unwanted parallel circuit which would cause condenser 52 of unit 37 to discharge into condenser 20 of unit 12 rather than in the desired path, that is, to transformer 3t When, on the other hand, unit 12 supplies the spark discharge for plug 36 and unit 37 is de-energized, the system is such as to prevent any substantial flow of current from unit 12 into unit 37. Thus under such conditions condenser 2t} is charged, as is also condenser 24 which is connected in parallel with condenser 20 through resistance 25 and the ground. When condensers 2t} and 24 are charged to a sufficiently high voltage, they discharge through control gap 22. The resulting pulse flows into lead wire 38, through the further gap 26 to wires 62, 59, and 51, and also flows through the primary 31 of transformer 30 to condenser 34 and thence to ground. This induces a high voltage in the secondary 32 of transformer 30 to ionize gap 36, the main portion of the pulse then flowing through secondary 32 to the spark gap 36. Since the distributed capacity of control gap 55 of unit 37 is small, the surge of current through lead wire 59 is insufdcient to form a voltage drop sufficient to ionize gap 55. Thus gap 55 acts as an effective barrier against the flow of any substantial amount of current from unit 12 into unit 37 when the ignition system is being powered by the former unit.

The embodiment of ignition system of the invention shown in FIG. 2 is generally the same as that of FIG. 1, except for the change of location of the barrier gap 26 and its shunting condenser 27. In the system of FIG. 1, gap 26 and condenser 27 are located within unit 12 whereas in the system of FIG. 2 gap 26 and condenser 27 are located within the alternating current supplied unit, there designated 37'. For clarity of illustration, the elements which are the same in the circuits of FIGS. 1 and 2 to the left of the line A-A of FIG. 1 have been omitted in FIG. 2.

In the circuit of FIG. 2 the direct current powered unit is designated 12'. Wire 38 from the output electrode of control gap 22 is connected to a shielded interconnecting lead 67 through a connector 65 on unit 12'. The other end of wire 67 is connected to unit 37' through a connector 69 thereon, the shield 65 for wire 67 being connected to the housings of the two units. The barrier gap 26 has its input electrode connected to lead wire 67 and its output electrode connected to wire 51 in unit 37'. Condenser 27 is shunted across gap 26, as shown.

Wire 51, beyond its connection to condenser 27, extends to a connector 7 t}, such connector having a shielded lead wire 74 extending therefrom to an input connector 71 on a further separate transformer unit 75. The shield 72 for Wire 74 is connected to the housings of units 37' and 75. Wire 74 is connected to one end of each of the primary 81 and the secondary 82 of a high frequency step-up transformer 86 within unit 75. Primary 81 is connected to ground through a condenser 79, the condenser being shunted by a resistance 77. The output terminal of secondary 82 of the step-up transformer extends to a connector 7-6 and thence to one terminal of igniter plug 36. The other terminal of plug 36 is connected to ground, as shown.

The circuit of FIG. 2 lends itself conveniently to use with existing systems having only a direct current powered ignition unit such as that shown at 12'. When such existing systems are modified in accordance with the invention, no changes need be made in unit 12. It is necessary only to add the units 37' and 75, and to connect units 12 and 37 by the lead wire 67.

Although only a limited number of embodiments of the invention have been illustrated in the accompanying drawings and described in the foregoing specification, it is to be especially understood that various changes, such as in the relative dimensions of the parts, materials used, and the like, as well as the suggested manner of use of the apparatus of the invention, may be made therein without departing from the spirit and scope of the invention as will now be apparent to those skilled in the art.

What is claimed is:

1. An ignition system for a combustion engine, comprising an igniter gap having electrodes, a first ignition unit, a first delivery circuit for applying the energy of said first unit to one of the electrodes of said igniter gap, said first delivery circuit including a control gap interposed between the first ignition unit and the igniter gap, a first storage condenser connected between the delivery circuit in advance of the control gap and another of the electrodes of the igniter gap, and a second condenser connected in shunt with the control gap, a second ignition unit, and a second delivery circuit for applying the energy of the second unit to said igniter gap, the first and second delivery circuits being connected between the control gap and the igniter gap, the first and second condensers forming a voltage divider which prevents the voltage applied to the control gap from reaching the breakdown voltage of the control gap when 6 the igniter gap is supplied with discharge energy from the second ignition unit.

2. An ignition system as claimed in claim 1, comprising a direct current power supply for the first ignition unit, and an alternating current power supply for the second ignition unit, and wherein the first ignition unit delivers relatively high electrical energy and the second ignition unit delivers relatively low electrical energy.

3. An ignition system for a combustion engine, comprising an igniter gap having electrodes, a first ignition unit, a first delivery circuit for applying the energy of said first unit to one of the electrodes of said igniter gap, said first delivery circuit including a control gap interposed between the first ignition unit and the igniter gap, a first, storage condenser connected between the de livery circuit in advance of the control gap and another of the electrodes of the igniter gap, a second condenser connected in shunt with the control gap, a barrier gap connected in series with the control gap in the first delivery circuit and between the control gap and the igniter gap, and a third condenser connected in shunt with the barrier gap, a second ignition unit, and a second delivery circuit for applying the energy of the second unit to said igniter gap, the first and second delivery circuits being connected between the barrier gap and the igniter gap, the first, second, and third condensers forming a voltage divider which prevents the voltage applied to the control gap from reaching the breakdown voltage of the series connected control and barrier gaps when the igniter gap is supplied with electrical discharge energy from the second ignition unit.

4. An ignition system as claimed in claim 3, comprising a direct current power supply for the first ignition unit, and an alternating current power supply for the second ignition unit, and wherein the first ignition unit delivers relatively high electrical energy and the second ignition unit delivers relatively low electrical energy.

5. An ignition system as claimed in claim 3, wherein the barrier gap has a breakdown voltage which is substantially lower than that of the control gap.

6. An ignition system for a combustion engine, comprising an igniter gap having electrodes, a first ignition unit, a first delivery circuit for applying the energy of said first unit to one of the electrodes of said igniter gap, said first delivery circuit including a control gap interposed between the first ignition unit and the igniter gap, a first, storage condenser connected between the delivery circuit in advance of the control gap and another of the electrodes of the igniter gap, and a second condenser connected in shunt with the control gap, a second ignition unit, and a second delivery circuit having a second control gap connected in series therein for applying the energy of the second unit to said igniter gap, the first and second delivery circuits being connected between'the control gap and the igniter gap, the first and second condensers forming a voltage divider which prevents the voltage applied to the control gap from reaching the breakdown voltage of the control gap when the igniter gap is supplied with discharge energy from the second ignition unit.

7. An ignition system as claimed in claim 6, wherein the second control gap has a breakdown voltage on the same order as that of the first control gap.

8. An ignition system as claimed in claim 7, comprising a barrier gap connected in series with the first control gap in the first delivery circuit and between the first control gap and the igniter gap, and a third condenser connected in shunt with the barrier gap, the first and second delivery circuits being connected between the barrier gap and the igniter gap, the first, second, and third condensers forming a voltage divider which prevents the voltage applied to the first control gap from reaching the breakdown voltage of the series connected first control gap and the barrier gap when the igniter gap is supplied with electrical discharge energy from the second ignition unit,

7 said barrier gap having a breakdown voltage which is substantially less than the breakdown voltages of the first and second control gaps.

9. An ignition system for a jet engine, comprising an igniter gap, a first, high energy ignition unit having a control gap and a first condenser shunting the control gap, means for applying the output of said high energy ignition unit to said igniter gap, a DC. supply, switch means connected between said D.C. supply and said high energy ignition unit, a second, low energy ignition unit, said low energy ignition unit being capable of continuous operation, the first and second ignition units being conected in advance of the igniter gap, whereby to apply the output of said low energy unit to said igniter gap, an A.C. supply, switch means connected between said A.C. supply and said low energy ignition unit, means for selectively closing the switches between the DC. and A.C. supplies and the high energy ignition unit and the low energy ignition unit, respectively, and means for preventing appreciable current fiow from each of the ignition units, when such unit is energized, into the other ignition unit, the means for preventing appreciable current flow from the second ignition unit when it is energized into the first ignition unit comprising a barrier gap and a second, shunting condenser interposed in the first ignition unit between the control gap of the first ignition unit and the point of connection of the first and second ignition units.

10. An ignition system for a combustion engine, comprising an igniter gap, a first ignition unit having a control gap, means for applying the energy of said first unit to said igniter gap, a DC. supply for said first ignition unit, switch means connected between said D.C. supply and said first igintion unit, a second ignition unit having a control gap, the first and second ignition units being connected in advance of the igniter gap, whereby to apply the output of said second unit to said igniter gap, an A.C. supply for the second ignition unit, switch means connected between said A.C. supply and said second ignition unit, means for opening the switch between the DC. supply and said first ignition unit when the switch between said A.C. supply and said second ignition unit is closed, and means for preventing appreciable current flow from each of the ignition units, when such unit is energized, into the other ignition unit, the means for preventing appreciable current flow from the second ignition unit when it is energized into the first ignition unit comprising a first condenser shunting the control gap, and a barrier gap and a second condenser shunting the barrier gap interposed in the first ignition unit between the control gap of the first unit and the point of connection of the first and second ignition units, and the means for preventing appreciable current flow from the first ignition unit when it is energized into the second ignition unit comprising the control gap in the second ignition unit.

11. An apparatus for use with a high energy ignition system having a first, high energy ignition unit, an i gniter gap having electrodes, a DC. supply, switch means connected between said D.C. supply and said high energy ignition unit, a first delivery circuit for applying the energy of said first unit to one of the electrodes of said igniter gap, said first delivery circuit including a control gap interposed between the first ignition unit and the igniter gap, a first, storage condenser connected between the delivery circuit in advance of the control gap and another of the electrodes of the igniter gap, and a second condenser connected in shunt with the control gap, a second, low energy ignition unit, said low energy ignition unit being capable of continuous operation, an A.C. supply, switchmeans connected between said A.C. supply and said low energy ignition unit, means for selectively closing the switches between the DC. and A.C. supplies and the high energy ignition unit and the low energy ignition unit, respectively, a second delivery circuit for applying the energy of the second unit to said igniter gap, the first and second delivery circuits being connected between the control gap and the igniter gap, the first and second condensers forming a voltage divider which prevents the voltage applied to the control gap from reaching the breakdown voltage of the control gap when the igniter gap is supplied with discharge energy from the second ignition unit.

12. Apparatus as claimed in claim 11, comprising a barrier gap connected in series with the control gap in the first delivery circuit and between the control gap and the igniter gap, and a third condenser connected in shunt with the barrier gap, the first and second delivery circuits being connected between the barrier gap and the igniter gap, the first, second, and third condensers forming a voltage divider which prevents the voltage applied to the control gap from reaching the breakdown voltage of the series connected control and barrier gaps when the igniter gap is supplied with electrical discharge energy from the second ignition unit.

13. An ignition system for supplying a spark discharge gap with a continuous succession of pulses of gap discharging voltage, comprising first and second sources of pulses for the discharge gap, said first source of pulses including a source of direct current and a first circuit connected to the source of direct current so as to be powered thereby, said first circuit being adapted for intermittent operation, said second source of pulses including a source of alternating current and a second circuit connected to the source of alternating current so as to be powered thereby, said second circuit being adapted for continuous operation, said first circuit including a vibrator for periodically interrupting the current in the first circuit fed thereto by the direct current source, a transformer having a primary and a secondary, the primary being connected to the output of the first circuit, the secondary being connected to supply the spark discharge gap, said second circuit including means fed by the alternating current source for producing current pulses, current rectifying means, a storage condenser, and a control gap, the output of the second circuit being connected to the primary of the transformer in parallel :with the output of the first circuit, current in the second circuit being rectified, stored in the storage condenser, and then fed to the control gap, the transformer, and the spark discharge gap, in that order, means selectively to energize the first source of pulses and means selectively to energize the second source of pulses, and

means including a condenser voltage divider in said first comprises a barrier gap and a shunting condenser interposed in the first circuit between the control gap in the first circuit and the point of connection of the transformer to the second circuit.

15. An ignition system as claimed in claim 14, wherein the discharge voltage of the control gap in the first circuit exceeds the discharge voltage of the barrier gap.

No references cited. 

1. AN IGNITION SYSTEM FOR A COMBUSTION ENGINE, COMPRISING AN IGNITER GAP HAVING ELECTRODES, A FIRST IGNITION UNIT, A FIRST DELIVERY CIRCUIT FOR APPLYING THE ENERGY OF SAID FIRST UNIT TO ONE OF THE ELECTRODES OF SAID IGNITER GAP, SAID FIRST DELIVERY CIRCUIT INCLUDING A CONTROL GAP INTERPOSED BETWEEN THE FIRST IGNITION UNIT AND THE IGNITER GAP, A FIRST STORAGE CONDENSER CONNECTED BETWEEN THE DELIVERY CIRCUIT IN ADVANCE OF THE CONTROL GAP AND ANOTHER OF THE ELECTRODES OF THE IGNITER GAP, AND A SECOND CONDENSER CONNECTED IN SHUNT WITH THE CONTROL GAP, A SECOND IGNITION UNIT, AND A SECOND DELIVERY CIRCUIT FOR APPLYING THE ENERGY OF THE SECOND UNIT TO SAID IGNITER GAP, THE FIRST AND SECOND DELIVERY CIRCUITS BEING CONNECTED BETWEEN THE CONTROL GAP AND THE IGNITER GAP, THE FIRST AND SECOND CONDENSERS FORMING A VOLTAGE DIVIDER WHICH PREVENTS THE VOLTAGE APPLIED TO THE CONTROL GAP FROM REACHING THE BREAKDOWN VOLTAGE OF THE CONTROL GAP WHEN THE IGNITER GAP IS SUPPLIED WITH DISCHARGE ENERGY FROM THE SECOND IGNITION UNIT. 